In some implementations, a method performed by data processing apparatuses includes receiving order data that represents a plurality of ordered items for delivery to a location; selecting a first policy from a store of first policies; transforming at least a portion of the order data into a plurality of item units, based on rules associated with the selected first policy; selecting a second policy from a store of second policies; for each item unit, based on rules associated with the selected second policy, modifying the item unit to include annotated information that corresponds to operations to be performed on the item unit; and generating instructions for grouping the plurality of item units for delivery to the location, based on the annotated information for the item units.